I want to have a screen (50% transparent white) pop up over an image on rollover with a button that, when pushed, will swap the image with a different one. Anyone know the easiest way to do this.

Javascript and CSS.

you can use the opacity/filter method for your transparency, or you can use a small .png image repeated as a background.

but just use hide and show layers for three layers on top of each other?

1: the original image
2: The screen and button
3: The second image